Colloids are known to transport contaminants over long distances in
natural media. Despite this potentially harmful effect, very few studies
have been undertaken in subsurface aquifers. This paper presents the
first results of a study of natural colloids and particles in a karstic
aquifer. The site was chosen for its coverage by clay layers and peat
which deliver various and numerous particle types in water. The
methodological part describes three methods used for size determination
and sample fractionation of surface water and spring water. These
methods have been adapted for the treatment of multiple samples due to
the rapid discharge variation typical of karstic aquifers. The analysis
of many particle size distributions (PSD) shows that they can be
described by a Pareto law. The variation of the slope of the PSD at the
spring is mainly dependent on discharge. This behavior is interpreted as
a washing of the karstic drains during the first phase of high flow
events. Fractionation of the samples allowed application of various
characterization techniques to particle size classes. X-ray diffraction
(XRD) patterns showed that most of the mineral particles originated from
Quaternary deposits and limestones. However the use of scanning electron
microscopy with energy-dispersive spectrometer (SEM-EDS) detailed the
composition of individual particles and revealed particles not found by
XRD. These techniques also showed the high complexity of the natural
particles and the important place of coprecipitation in their formation.
Consequences on the fluxes of particulate matter and its potential role
as a carrier of contaminants are discussed.